A shield support for underground mining operations having a roof bar pivotally mounted on the upper end of a caving shield and laterally extensible aperture sealing plates of L-section arranged along opposite sides of the roof bar and opposite sides of the caving shield, the plates on the roof bar extending back to the rearward edge of the roof bar and the plates on the caving shield extending no further forward than the arc described by the rearward end of the roof bar plates upon pivoting of the roof bar relative to the caving shield.